Electrical connection for nonmetallic resistors



Feb. 7, 1933. A- H HEYROTH 1,897,004

ELECTRICAL CONNECTION FOR NONMETALLIC HESISTORS Filed Jan. 19, 1931 2 Smets-sheet 2 l/ /1 /l/ if,

INVENTOR ALBERT HMEYRMH ATTORNEY Patented Feb. 7, 1933 UNITED STATES PATENT OFFICE ALBERT H. HEYBOTH, OF NIAGARA FALLS, NEW YORK', ASSIGNOR TO THE GLOBA'B CORPORATION, OF NIAGARA FALLS, NEW YORK ELECTRICAL CONNECTION FOR NONMETALJIC RESISTORS Application med :anual-y19, 1931. serial No. 509,598.v

The invention relates to electric furnaces having rigid non-metallic resistors and to improved methods of making electrical connections therein. The invention is particularly applicable to furnaces employing silicon carbide resistors.

In the use of silicon carbide resistors the elements can be placed directly within the furnace chamber, and it is customary to make electrical contact by means of metallic terminal members extending through the furnace wall. These terminals also function as a means ofsupport for the element, and are so positioned that the metallic surface in contact with the end of the resistor is comparatively close to the inner wall of the furnace chamber. In high temperature furnaces the metal is thus exposed to intense heat and, in addition, there is `always considerable arcing at the points of areas of contact with the resistor.

If it were attempted to operate a metallic contact of this character without water cooling, the terminal would have a very short life. On the other hand, the introduction of water cooling causes considerable heat loss, since the terminal extends into the hotter portion of the furnace. vMeasurements made with the type of terminals usually employed have shown that the heat loss due to water cooling may be an appreciable part of the total power consumed.

In the electric furnaces described herein, I employ two or more rigid non-metallic resistors, and make electrical connections between the ends of two adjacent resistors b means of a conducting material which is su ciently refractory so that it can be placed entirely within the furnace chamber. Owing to the fact that silicon carbide resistors are operated in air without protectionfrom oxidation, oxidizable materials such as carbon and graphite, which are both highly conducting and refractory, cannot be used. Metals are also impractical when placed entirely within the furnace because ot their comparativel low melting points, their oxidizability an their inability to withstand the arcing which takes place at the ends of the resistor. I have found that a connector composed of a material which I will designate as a siliconized silicon carbide can be placed entirely within the furnace chamber without causing deterioration of the contact. A furnace containing such a connecting member can ,be operated for prolonged periods of time at temperatures up to 1400 degrees centigrade withouta-ppreciable oxidation of the contact material. The electrical conductivity of the siliconized material is sufficiently great in comparison with that of the resistor so that very little heat is generated by the passage of the current through the terminal .or Aconnecting members. The size of the connectors can also be regulated so as to afford a minimum of electrical resistance.

The introduction of a connecting member which can be placed entirely within the furnace chamber makes possible the connection of two or more resistors 'in series with only half the usual number of external terminals.

If Water cooled metal terminals are used for the external contacting members, the heat loss caused by water cooling is reduced to half of that which would otherwise obtain. The element and the connecting members are much more readily replaced than is the case when the usual terminal mounting is employed at each end of the resistor.

In many furnacel installations employing external terminals for each end of the resistor,

the terminal mountings are either inaccessible or occupy space which could be advantageously used for other purposes. As examples of such installations, there are many furmembers and the method of employing them ings, in which will be evident from the accompanying draw- Fi 1 shows a sectional view of an electric ace in which two resistor elements are connected in series-by means of a siliconized silicon carbide connector;

Figure 2 shows a section of the furnace shown in Figure 1, the section being Vtaken along the lines Il-II;

Fi re 3^shows a sectional view of a furnace 1n which the elements are mounted ver? tically, the internal'connector resting on the.

floor of the furnace and being readily replaceable; and

Figure 4f shows a sectional view of a mumsv furnace in which the resistors are placed outside the heating chamber and the resistors connected by means of a connector at'the rear of the furnace.v

ferring to Figures 1 and 2, the silicon carbide resistors 1 are supported by\resilient butt-end engagement with the terminal membersV 2. These terminal members may be water cooled as indicated, the inlet and outylbetpassages connected with the water system em designated by 3 and fl respectively. The mlet passage 3 is connected with the tube 9 so that the cooling fluid impinges upon the metal terminal facing 8. The water connections are made through the cap 5 which forms the extremity of the terminal. `Pressure against the ends of the silicon carbide resistors is afforded by the springs 12. The termidesirable that the connectors be provided with recesses 7 for engagement with the ends of the resistors.

Any method of resilient mounting can be used for ositioning the external terminals and for a ording pressure against the ends'of the resistor rods` ln the method shown 'in Figure 2, the ,lever 10'is forced against the terminal 2 by means of the spring 12. The

lever Y10 `possesses a recessed portion 11 at the opposite end from the portion adapted to engagewith the terminal member 9. This recessed portion 11 engages with the bracket ,13,

4which 1s 'mounted on the wall of the furnace. rlhe e'ect is thus the same as if the lever 10 were pivoted at the recessed portion 11. The

'bushin for the terminal. Wit the connectorL shown in Figure 3, the

metal terminal facing 8 is recessed at 15 so as to engage with the end of the resistor 1. The recess may be either cup shaped or conical. A refractory tube 16 may be used asa projecting portions 18 are ada ted to iit into corresponding cavities in thelb ottom of the of heat, or to protectpthe resistor from in- 'I jurious substances present within the heating chamber. In such cases, it is also advantageous to use a siliconized silicon carbide connector to eliminate a portion of the externalterminal members.

A. furnaceo this type is shown in Figure 4. rlhe inner muiiie 20 is( preferably composed of a material havin a high'thermal conductivity as, for examp e, silicon carbide or `fused alumina. The connector 21 is positioned in the rear wall of the furnace. The necessity of external terminal mountin s in the rear of the furnace is thus eliminated.

B siliconizedsilicon carbide I mean lany pro uct wherein silicon carbide is impre -v nated or alloyed with silicon. These pro ucts vary somewhat` in structure and constitution, depending upon the method of manufacture. Aspecific type of material which has been found to be very satisfactory is described in a copending a plication, United States Serial No. 382,004 gled July 29, 1929. In the manufacture of the materialin accordance with the process described in the y above copending application, a heat hard- ,ened silicon carbide article, as for example4 one made by the process known as recrystallization, is surrounded with a small excess of molten silicon over that required for impregnation and the article and the surrounding silicon are then heated to a temperature at which the silicon rapidly vaporizes. The heating is eEected as rapidly as possible and the excess silicon is removed n, by vaporisation. The original form of the article is v preserved intact without the adherence of globules of excess metal.y After the excess silicon has been removed by vaporization, the article maybe heated at a temperature above the boiling point of silicon for a very short time, usually about 30 seconds, in order to secure a more complete alloying action. The electrical resistance of the product is considerably decreased bythe additional heating after the removal ofthe excess silicon metal. y I A The product as prepared above is believed to be an alloy of silicon and silicon carbide.`

Microscopic evidence indicates that the silicon dissolves the smaller particles of silicon carbide and also dissolves a portion of th surface of the larger particles.

When siliconized silicon carbide connectors are employed in combination with silicon carbide resistors suchV as are sold under the trade name of Global-7, in Awhich the terminal portions 'of 'the element are also siliconized, I have found that the arcing which takes place at high temperatures produces a sli ht welding action between the connector an the end portion of the resistor. This weld does not have sulliciently great mechanical strength to interfere with the removal of the element, but it does produce a more effective electrical contact, and greatly minimizes any disintegration at the area of contact from arcing.

Various forms and modifications of the connector above described may be used to meet particular conditions. By connector is meant any member which Will afford electrical connection between two or more resistors, and which can be placed entirely within an electric furnace.

I claim: y y

1. A siliconized silicon carbide connector for rigid non-metallic resistors, the said connector having depressions adapted to receive the ends of the resistors.

2. A siliconized silicon carbide connector for non-metallic resistors, the said connector having projections which are adapted to fit into corresponding cavities in the wall of an electric furnace.

3. In an electric furnace, a plurality of silicon carbide resistors and a connecting member of siliconized silicon carbide within the furnace chamber.

4. In an electricV furnace, a plurality of silicon carbide` resistors and a connecting member of siliconized silicon carbide within the furnace, said connecting member being positioned in a cavity within the inner wall of the electric furnace.

5. In an electric furnace, a plurality of silicon carbide resistors and a connectin 40 member of siliconized silicon carbide, the

said connecting member being held in position bgd pressure transmitted through the resistor r s.

6. The method of electrically connecting silicon carbide resistors which comprises forcing adjacent ends of two resistors against a connecting member of siliconized silicon carbide by resilient pressure.

7. The method of electrically connecting non-metallic resistors which comprises connecting two resistors in series through an intermediary connecting member of siliconized silicon carbide.

8. The method of electrically connecting silicon carbide resistors having siliconized ends, which comprises forcing the end of the resistor against a siliconized silicon carbide connecting member and effecting a temporary weld between the end of the resistor and the said connecting member.

In testimony whereof .I ax m atu. ALBERT H. 

